System and Method for Uplink Grant-Free Transmission Scheme

ABSTRACT

A method embodiment includes implementing, by a base station (BS), a grant-free uplink transmission scheme. The grant-free uplink transmission scheme defines a first contention transmission unit (CTU) access region in a time-frequency domain, defines a plurality of CTUs, defines a default CTU mapping scheme by mapping at least some of the plurality of CTUs to the first CTU access region, and defines a default user equipment (UE) mapping scheme by defining rules for mapping a plurality of UEs to the plurality of CTUs.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/790,673, entitled “System and Method for Uplink Grant-FeeTransmission Scheme,” filed on Mar. 8, 2013, which application is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a system and method for wirelesscommunications, and, in particular embodiments, to a system and methodfor uplink grant-free transmission scheme.

BACKGROUND

In a typical wireless network such as long-term evolution (LTE) network,the selection of shared data channels for uplink (UL) isscheduling/grant based, and the scheduling and grant mechanisms arecontrolled by a base station (BS) in a network. A user equipment (UE)sends an UL scheduling request to the base station. When the BS receivesthe scheduling request, the BS sends an UL grant to the UE indicatingits UL resource allocation. The UE then transmits data on the grantedresource.

An issue with this approach is that the signaling resource overhead forthe scheduling/grant mechanism can be quite large, especially in caseswhere the data transmitted is small. For example, for small packettransmissions of around 20 bytes each, the resources used by thescheduling/grant mechanism could be around 30%, or even 50%, of thepacket's size. Another issue with this approach is the scheduling/grantprocedure causes an initial delay in data transmission. Even when theresources are available, there is a minimum 7-8 ms delay in a typicalwireless network between a scheduling request being sent and the firstuplink data transmission.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present invention which provide a system and method for uplinkgrant-free transmission scheme.

In accordance with an embodiment, a method includes implementing, by aBS, a grant-free uplink transmission scheme. The grant-free uplinktransmission scheme defines a first contention transmission unit (CTU)access region in a time-frequency domain, defines a plurality of CTUs,defines a default CTU mapping scheme by mapping at least some of theplurality of CTUs to the first CTU access region, and defines a defaultuser equipment (UE) mapping scheme by defining rules for mapping aplurality of UEs to the plurality of CTUs.

In accordance with another embodiment, a base station (BS) includes aprocessor, and a computer readable storage medium storing programmingfor execution by the processor, the programming including instructionsto implement a grant-free uplink transmission scheme, receive an uplinktransmission from a user equipment (UE), attempt to decode the uplinktransmission blindly, and indicate to the UE whether the attempt todecode the uplink transmission blindly was successful. The grant-freeuplink transmission scheme defines a plurality of contentiontransmission units (CTUs), defines one or more CTU access regions in atime-frequency domain, creates a default CTU mapping scheme by mappingthe plurality of CTUs to the one or more CTU access regions, and createsa default UE mapping scheme by defining rules for mapping a plurality ofUEs to the plurality of CTUs.

In accordance with another embodiment, a method for a grant-freetransmission scheme includes implementing, by a user equipment (UE), adefault contention transmission unit (CTU) mapping scheme by determiningan appropriate CTU for uplink transmission in accordance with a UEmapping rule and the default CTU mapping scheme, and transmitting anuplink transmission, to a base station (BS), on the appropriate CTU.

In accordance with yet another embodiment, a user equipment (UE)includes a processor, and a computer readable storage medium storingprogramming for execution by the processor, the programming includinginstructions to implement a default contention transmission unit (CTU)mapping scheme by determining an appropriate CTU for uplink transmissionin accordance with a UE mapping rule and the default CTU mapping scheme,and transmitting, to a base station (BS), an uplink transmission on theappropriate CTU, determine whether a collision has occurred based on anindication by the BS, and re-transmit, to the BS, the uplinktransmission using an asynchronous hybrid automatic repeat request(HARQ) mechanism when the UE determines a collision has occurred.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawing, in which:

FIG. 1 is a block diagram illustrating a network in accordance withvarious embodiments;

FIG. 2 is a diagram illustrating an example configuration of variouscontention transmission (CTU) access regions in accordance with variousembodiments;

FIG. 3 is a diagram illustrating an example mapping of CTUs to CTUaccess regions in accordance with various embodiments;

FIG. 4 is a diagram illustrating an example CTU index numbering inaccordance with various embodiments;

FIGS. 5A and 5B are diagrams illustrating an example UE mapping andremapping in accordance with various embodiments;

FIG. 6 is a block diagram of a joint signature and data detection usingmessage passing algorithm method with an active UE detector inaccordance with various embodiments;

FIGS. 7A and 7B are flow diagrams of base station (BS) activity inaccordance with various embodiments;

FIGS. 8A and 8B are flow diagrams of user equipment (UE) activity inaccordance with various embodiments; and

FIG. 9 is a block diagram illustrating a computing platform that may beused for implementing, for example, the devices and methods describedherein, in accordance with an embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of embodiments are discussed in detail below. Itshould be appreciated, however, that the present invention provides manyapplicable inventive concepts that can be embodied in a wide variety ofspecific contexts. The specific embodiments discussed are merelyillustrative of specific ways to make and use the invention, and do notlimit the scope of the invention.

Various embodiments are described with respect to a specific context,namely a LTE wireless communication network. Various embodiments mayalso be applied, however, to other wireless networks such as a worldwideinteroperability for microwave access (WiMAX) network.

FIG. 1 illustrates a block diagram of a network 100 according to variousembodiments. A base station (BS) 102 manages uplink and downlinkcommunications for various UEs 104-114 within its coverage area 116. BS102 may alternatively be referred to as a cell tower, an eNodeB, anaccess network, and the like. BS 102 may support transmissions formultiple cellular carriers concurrently. BS 102 implements a grant-freeuplink transmission scheme, wherein contention transmission unit (CTU)access regions are defined so that UEs 104-114 may contend for andaccess uplink resources without a request/grant mechanism. Thegrant-free uplink transmission scheme may be defined by the BS, or itmay be set in a wireless standard (e.g., 3GPP). UEs 104-114 may bemapped to various CTU access regions to avoid collision (i.e., when twoor more UEs attempt to transmit data on the same uplink resource).However, if collision occurs, UEs 104-114 may resolve collisions usingan asynchronous HARQ (hybrid automatic repeat request) method. BS 102blindly (i.e., without explicit signaling) detects active UEs anddecodes received uplink transmissions.

Under this scheme, UEs 104-114 may send uplink transmissions without theBS allocating resources to request/grant mechanisms. Therefore, totalnetwork overhead resources are saved. Furthermore, this system allowsfor time savings during uplink by bypassing the request/grant scheme.Although only one BS 102 and six UEs 104-114 are illustrated in FIG. 1,a typical network may include multiple BS each covering transmissionsfrom a varying multitude of UEs in its geographic coverage area.

Network 100 uses various high level signaling mechanisms to enable andconfigure grant-free transmissions. UEs 104-114 capable of grant-freetransmissions signal this capability to BS 102. This allows BS 102 tosupport both grant-free transmissions and traditional signal/granttransmissions (e.g., for older UE models) simultaneously. The relevantUEs may signal this capability by, for example, RRC (radio resourcecontrol) signaling defined in the 3GPP (third generation partnershipproject) standard. A new field may be added to the UE capability list inRRC signaling to indicate whether the UE supports grant-freetransmissions. Alternatively, one or more existing fields can bemodified or inferred from in order to indicate grant-free support.

BS 102 also uses high-level mechanisms (e.g., a broadcast channel or aslow signaling channel) to notify UEs 104-114 of information necessaryto enable and configure a grant-free transmission scheme. For example,BS 102 may signal that it supports grant-free transmissions, its searchspace and access codes for CTU access regions, a maximum size of asignature set (i.e., the total number of signatures defined), amodulation and coding scheme (MCS) setting, and the like. Furthermore,BS 102 may update this information from time to time using, for example,a slow signaling channel (e.g., a signaling channel that only occurs inthe order of hundreds of milliseconds instead of occurring in everyTTI).

BS 102 implements a grant-free uplink transmission scheme. Thegrant-free transmission uplink scheme defines CTU access regions toenable grant-free transmissions by UE 104-114. A CTU is a basicresource, predefined by network 100, for contention transmissions. EachCTU may be a combination of time, frequency, code-domain, and/or pilotelements. Code-domain elements may be CDMA (code division multipleaccess) codes, LDS (low-density signature) signatures, SCMA (sparse codemultiple access) codebooks, and the like. These possible code-domainelements are referred to generically as “signatures” hereinafter.Multiple UEs may contend for the same CTU. The size of a CTU is presetby the network and may take into account an expected transmission size,the amount of desired padding, and/or MCS levels.

A CTU access region is a time-frequency region where contentiontransmission occurs. The grant-free uplink transmission scheme maydefine multiple CTU access regions for network 100. The grant-freetransmission uplink scheme may be defined by BS 102 via high levelsignaling (e.g., through a broadcast channel) or it may be pre-definedby a standard and implemented in UEs (e.g., in a UE's firmware). Theregions may exist in one or more frequency bands (intra-band orinter-band) and may occupy the entire uplink transmission bandwidth or aportion of the total transmission bandwidth of BS 102 or a carriersupported by BS 102. A CTU access region that occupies only a portion ofthe bandwidth allows BS 102 to simultaneously support uplinktransmissions under a traditional request/grant scheme (e.g., for olderUE models that cannot support grant-free transmissions). Furthermore, BS102 may utilize unused CTUs for scheduled transmissions under arequest/grant scheme, or BS 102 may adjust the size of CTU accessregions if portions of the access regions are not used for a period oftime. Furthermore, the CTU access regions may frequency hopperiodically. BS 102 may signal these changes in CTU access region sizeand frequency to UEs 104-114 through a slow signaling channel.

FIG. 2 illustrates an example configuration for various CTU accessregions defined by BS 102. In FIG. 2, BS 102 supports transmissions forthree carriers each operating at frequencies F₁, F₂ and F₃ withbandwidth BW₁, BW₂ and BW₃. FIG. 2 illustrates example CTU accessregions 200 defined in all three carriers using differentconfigurations. The configurations shown in FIG. 2 are for illustrativepurposes only, and alternative CTU access region configurations may bedefined in various embodiments.

Multiple CTU access regions (e.g., as illustrated in FIG. 2) allow eachCTU access region to be categorized differently to provide differenttypes of service to varying UE types. For example, the CTU accessregions may be categorized to support different quality of service (QoS)levels, different UE configurations (e.g., in situations of carrieraggregation), different UE subscribed levels of service, different UEgeometries, or a combination thereof. Furthermore, each CTU accessregion may be configured to support a different number of UEs. The sizeof each CTU access region may vary depending on the expected number ofUEs using the region. For example, the size of a CTU access region maybe based the history of loading in the CTU access region (such as thenumber of UEs), UE collision probability estimations, and/or measured UEcollisions over a period of time.

FIG. 3 illustrates an example CTU resource definition in various CTUaccess regions. FIG. 3 illustrates four CTU access regions 302-308. Theavailable bandwidth is divided into time-frequency regions for CTUaccess region 302-308, with each access region 302-308 occupying apredefined number of resource blocks (e.g., access region 302 occupiesRBs 1-4) of bandwidth. In FIG. 3, CTUs are mapped identically to accessregions 302-308, but varying views of this mapping are shown forillustrative purposes.

In FIG. 3, each CTU access region is capable of supporting up tothirty-six UEs contending for the thirty-six CTUs defined in eachregion. Each CTU is a combination of time, frequency, signature, andpilot. Each access region 302-308 occupies a distinct frequency-timeregion. These frequency-time regions are further broken down to eachsupport six signatures (S₁-S₆) and six pilots mapped to each signatureto create thirty-six total pilots (P₁-P₃₆). A pilot/signaturedecorrelator at BS 102 is used to detect and decode individual UEsignals and transmissions.

Therefore, under this scheme different UEs conduct uplink transmissionson the same signature. Various embodiments support signature collisions(i.e., when several UEs simultaneously access the same frequency-timeresources by using the same signature). In the known art, it waspreviously believed that signature collisions irreparably degrade UEperformance and should be absolutely avoided. However, it has beenobserved that while signature collisions may degrade UE performance, thetransmitted information can still be decoded by BS 102 using variousdecoding schemes (e.g., a JMPA scheme as described in detail insubsequent paragraphs). Furthermore, it has also been observed thatsignature collisions between two UEs (e.g., UEs 104 and 106) do notaffect the performance of other UEs (e.g., UEs 108-114). Therefore,signature collisions are not detrimental to overall system performance.Various embodiments map multiple potential UEs to the samefrequency-time-signature resource so that, at each contentiontransmission, the system may be fully loaded.

In contrast, pilot collisions may not be supported. Similar to signaturecollision, pilot collision refers to cases when multiple UEssimultaneously access the same frequency-time-signature resources byusing the same pilot sequence. However, unlike signature collisions,pilot collisions may lead to irreparable results in a grant-freetransmission scheme. This is due to BS 102 being unable to decode a UE'stransmission information in pilot collision scenarios because BS 102'sis unable to estimate the individual channels of UEs using the samepilot. For example, assume two UEs (UE 104 and 106) have the same pilotand their channels are h₁ and h₂, then BS 102 can only estimate achannel of quality of h₁+h₂ for both UEs 104 and 106. Thus, thetransmitted information will not be decoded correctly. Variousembodiments may define a number of unique pilots (e.g. thirty-six pilotsper access region in FIG. 3) depending on the number of UEs supported inthe system. The specific numbers given in FIG. 3 are for illustrativepurposes only, and the specific configuration of the CTU access regionsand CTUs may vary depending on the network.

Various embodiments enable grant-free transmissions through theinclusion of mechanisms for collision avoidance through UE to CTUmapping/re-mapping and collision resolution through asynchronous HARQ.For a UE to successfully perform uplink transmissions in a grant-freescheme, the UE must determine a CTU on which data can be sent. A UEdetermines the CTU it should use for transmissions based on predefinedmapping rules known by both the UE (e.g., UEs 104-114) and the basestations (e.g., BS 102) in a network (e.g., network 100). These mappingrules may be implicit (i.e., default) rules pre-defined for the UE (e.g.in an applicable standard or in the firmware of the UE) and/or explicitrules defined by a BS using high level signaling. For example, differentmapping rules (as referred to as mapping configurations) are pre-definedin a wireless standard, such as 3GPP, and the index of the applicablemapping configuration is signaled to a UE by the BS.

The grant-free uplink transmission scheme assigns a unique, identifyingCTU index, I_(CTU), to each CTU in the CTU access regions. UEs determinewhich CTUs to transmit on based on mapping rules for choosing anappropriate CTU index. The mapping of CTU indexes may be distributeduniformly over the available resources taking into account the size ofthe CTU regions over the time-frequency domain and the desire to reduceBS decoding complexity. The size of the CTU regions is taken intoaccount so that UEs are not mapped to the same subset of availabletime-frequency resources.

For example, FIG. 4 illustrates such a distribution of CTU indexes overthe CTU access regions. Each signature-pilot grid 402-408 corresponds toa time-frequency access region 302-308 from FIG. 3. As shown in FIG. 4,indexes are distributed in the following order: time, frequency,signature, and then pilot. For example, index 0 is mapped to a firsttime and a first frequency. Index 1 is then mapped to a second time inthe first frequency. Index 2 is mapped to the first time in a secondfrequency, and index 3 is mapped to the second time in the secondfrequency. Only when all the time-frequency combinations are exhaustedis the next index (index 4) mapped to a different signature in the firsttime and first frequency. In this manner all 144 CTU indexes (i.e., fouraccess regions multiplied by thirty-six pilots per region) are mapped todistribute UEs over the region and reduce the chance of signature andpilot collision. Various alternative embodiments may use differentmapping rules for CTU index mapping.

The inclusion of default mapping rules allows a UE to automaticallytransmit data on the mapped CTU as soon as it enters a BS's coveragearea without additional signaling. These default mapping rules may bebased on a UE's dedicated connection signature (DCS), its DCS indexassigned by a BS, the total number of CTUs, and/or other parameters suchas subframe number. For example, a UE i may map to a CTU resource index,I_(CTU) based on a default formula:

I _(CTU) =DSC _(i) mod N _(CTU)

wherein N_(CTU) represents the total number of available CTU indexes(e.g., 144 in the examples given in FIGS. 3-4) and DSC_(i) is the DSCindex of UE i.

A UE's DCS index may be assigned to the UE by a BS via high levelsignaling (e.g., through a broadcast, multicast, or unicast channel).Furthermore, this DCS index number may be used in conjunction with CTUindex mapping to evenly distribute UEs across the CTU access regions.For example, when a UE enters a BS's (e.g., BS 102) coverage area, theBS may receive notice of the UE entering its area. BS 102 may assign aDCS index (hence the DSC) to the UE. For example, the first UE isassigned DCS₁=0, the second UE is assigned DCS₂=1, the third UE isassigned DCS₃=2, and so on. When the UE maps to a CTU resource based ona default mapping formula (e.g., I_(CTU)=DSC_(i) mod N_(CTU)), the UEswill be assigned indexes based on their DCS index and the total numberof CTUs. By combining this mapping formula with the appropriate CTUindex mapping (e.g., FIG. 4), the UEs may be distributed evenly acrossthe CTU access regions. That is, the first UE will be mapped to index 0,the second UE will be mapped to index 1, etc.

A subset of UEs may be re-mapped periodically by the network to reducecollisions. UEs may be remapped in cases when UEs exchange packetsfrequently in a data session (referred to as active UEs). These activeUEs may experience higher probabilities of collision when they areunevenly distributed across the available CTU access regions. Forexample, FIG. 5A illustrates various UEs 502-516 mapped to four CTUaccess regions 518-524 under default mapping rules. In FIG. 5A, UEs 502,504, 514, and 516 are active UEs mapped to two of the four available CTUaccess regions, increasing their probability for collision. A BSassociated with the UEs (e.g., BS 102) determines that the defaultmapping is causing too many collisions and remaps certain UEs (e.g., UE504 and 514) to the other CTU access regions as shown in FIG. 5B. BS 102may detect the high level of collisions through high level signalingfrom the UEs or through repeated failed attempts to decode transmittedinformation (i.e., as previously discussed, pilot collisions causefailed attempts to decode transmission data). Alternatively, active UEsmay be initially mapped to the same CTU in an access region. When the BSdetermines collisions are occurring due to this mapping, the active UEsmay be re-mapped to different CTUs in the same access region. Thevarious UEs 502-516 may revert to default mapping rules eitherimplicitly when the UEs are no longer active or explicitly throughnetwork signaling. In alternative embodiments, this type of temporaryre-mapping may also be used to provide certain UEs with dedicatedresources for very time-sensitive transmissions when requested by the UEor configured by the network.

By implementing the described UE mapping strategies, the number ofinitial collisions in a CTU access region may be controlled. However,collisions may still occur and must be resolved. When transmissions aresuccessful, the UE will be notified by the BS through, for example, anACK (acknowledgement) signal. The BS only sends the ACK signal whentransmissions are successful. Therefore, if a UE does not receive an ACKsignal within a predetermined time period, the UE determines thatcollision has occurred. Alternatively, the BS may receive an NACK(negative acknowledgement)] signal when the transmission fails. The UEassumes transmission was successful unless it receives a NACK.

When collisions occur, they are resolved using asynchronous HARQmethods. Asynchronous HARQ methods differ from synchronous HARQ methodsin that the UE does not attempt to retransmit on the same CTU whencollision occurs. Rather the UE may choose a different CTU to retransmiton. For example, a random backoff procedure may be implemented. Each UEpicks a backoff time period (e.g., a next TTI) randomly within acontention window to retransmit data. At the next TTI, the UE transmitsdata. The contention window size is a system parameter that may besignaled to the UE using high-level signaling.

When BS 102 receives transmitted information, it blindly decodes thetransmitted information (referred to as blindly because BS 102 does notknow which UE transmitted the information or which UEs are active in anetwork). For example, BS 102 may use JMPA (joint signature and datadetection using MPA (message passing algorithm)) methods to blindlydecode the transmitted information. Generally, MPA methods rely onchannel knowledge and user-specific information to detect and decodedata. JMPA initially assume all possible users might be active. It theniteratively detects the active users and simultaneously tries to detecttheir transmitted data. At the end of the iteration, among the allpossible user pool, a list of active users and their detected data areprovided by JMPA. A detailed description of a JMPA system and method maybe found in U.S. Provisional Application No. 61/737,601, filed on Dec.14, 2012, entitled “System and Method for Low Density SpreadingModulation Detection,” which application is hereby incorporated hereinby reference.

An issue with this JMPA approach is that the original user pool might bevery large to start with. It may make the complexity of the JMPA processimpractically high. FIG. 6 illustrates a block diagram of a JMPAdetector 602, channel estimator 604, with an active UE detector 606 tosimplify the potentially high complexity of the JMPA process. A list ofall potential UEs is fed into JMPA detector 602, channel estimator 604,and active UE detector 606. Active UE detector 606 uses the list of allpotential UEs and received transmission data (e.g., all transmissionsreceived by the BS from the CTU access regions) to generate a smallerlist of potential active UEs. For example, as previously discussedmultiple pilots may be correlated with each signature. Therefore, ifactive UE detector 606 determines a signature is not active, allcorresponding pilots (i.e., CTU indexes/potential UEs) correlated withthe inactive signature are also inactive. These pilots are removed fromthe list of potential UEs. If active UE detector 606 determines a pilotis inactive, it is taken off the list as well. In this manner, active UEdetector 606 may decrease the list of potential active UEs for channelestimator 604 and JMPA detector 602, simplifying the decoding process.Furthermore, JMPA detector 602 may feed an updated list of potentiallyactive UEs back to active UE detector 606. For example, JMPA detector602 may determine that a second signature is inactive; this informationis fed back to active UE detector 606 so that the corresponding pilotsrelated to the second signature may be eliminated from the list ofpotential UEs.

Typically, uplink transmission performance depends on the number of theactive signatures. A fewer number of overlaid signatures correlates tobetter expected performance from a MPA detector, such as the JMPAdetector. This idea can be used to implicitly control the uplinkquality. Based on long-term traffic statistics and the number of thepotential active users, the network can statistically control theaverage number of the users transmitting within the same CTU accessregion. For example, different numbers of UEs can be grouped together toaccess different CTU access regions. The network can also limit thenumber of pilots and/or signatures in a CTU access region. If thechannel quality of the UEs is historically good, more interferencewithin a CTU access region may be tolerated (i.e., more of these UEs canbe configured to access a CTU access region allow for more pilots and/orsignatures to be defined). This long-term link-adaptation mechanism iscontrolled by the network through the defining of CTU access regions andthe mapping of UEs to access regions.

FIG. 7A illustrates a flow diagram of network activity (e.g., through BS102) according to various embodiments. In step 702, BS 102 defines CTUaccess regions. In step 704, BS 102 maps various CTU indexes to the CTUaccess region. Each CTU index corresponds to a CTU a UE (e.g., UE 104)may perform grant-free transmissions on. In step 706, BS 102 useshigh-level signaling (e.g., through a broadcast channel) to sendinformation enabling grant-free transmissions. This high-level signalingincludes information on the defined CTU access regions, number of CTUsin the access regions and/or CTU index map. The high-level signaling mayalso include assigned DCS index information, and the like.

Steps 702-706 illustrate BS 102 defining and implementing a grant-freeuplink transmission scheme. Alternatively, BS 102 may perform none or asubset of steps 702-706 because certain steps are pre-configured for BS102 by a standard. For example, a standard may eliminate step 702 bypre-defining CTU access regions. BS 102 need only perform steps 704 and706 (i.e., mapping CTU indexes to the CTU access regions andtransmitting information). In another example, a standard defines thegrant-free uplink transmission scheme and BS 102 need only implement thegrant-free uplink transmission scheme.

In step 708, BS 102 receives an uplink transmission from UE 104. In step710, the BS decodes the uplink transmission information blindly using,for example, a JMPA and active UE detector method. In step 712, BS 102determines whether the decoding was successful. If not, BS 102 assumesthat collision has occurred, and waits to receive another uplinktransmission. BS 102 also indicates to UE 104 whether the decoding wassuccessful. BS 102 may do this by sending an ACK signal only if thetransmission is successfully decoded. Alternatively, BS 102 may send aNACK signal if the transmission was not successfully decoded.

In an alternative embodiment illustrated in FIG. 7B, if decoding was notsuccessful in step 712, BS 102 determines if the number of faileddecodings (i.e., collisions) is above a certain configurable threshold.If not, BS 102 waits for the next transmission. If the number offailures meets a certain threshold, BS 102 uses this information andoverall conditions (e.g. distribution of active UEs in the CTUs) to makedecision on remapping the UEs to other CTU indexes in the same or adifferent CTU access region in step 718. BS 102 then returns to step 706to send the remapped CTU information via high-level signaling (e.g.,broadcast, multicast, or unicast) to the UEs in its coverage area.

FIG. 8A illustrates a flow diagram of UE activity in accordance withvarious embodiments. In step 802, UE (e.g., UE 104) enters a BS'scoverage area. In step 804, UE 104 receives high-level signalinginformation from the BS. This high level signaling information includesCTU access region definitions, total number of CTUs, default mappingrules, and the like. Alternatively, UE 104 may be preconfigured withdefault mapping rules. In step 806, UE 104 determines an appropriate CTUto conduct uplink transmissions on (e.g., UE 104 may determine anappropriate CTU index using default mapping rules).

In Step 808, UE 104 transmits information on the appropriate CTU. Instep 810, UE 104 determines whether collision has occurred based on anindication from the BS. For example, the UE may wait a predeterminedamount of time for an ACK signal. If an ACK signal is received, then instep 812, the uplink procedure is concluded and UE 104 moves on to itsnext task. If no ACK signal is received, UE 104 determines thatcollision has occurred, and moves to step 814. In step 814, UE 104resolves the collision using an asynchronous HARQ method. Alternatively,UE 104 assumes no collision has occurred unless it receives a NACK. If aNACK is received, the UE then continues with the collision resolutionprocedure.

In an alternative embodiment illustrated in FIG. 8B, if UE 104determines collision has occurred, UE 104 then determines if the numberof collisions exceed a certain threshold. If not, then UE 104 returns tostep 814 and resolves the collision using an asynchronous HARQ method.If the threshold is met, then in step 818, UE 104 may request remappingof CTUs by the BS. UE 104 then returns to step 804 and waits to receivethe remapping information form the BS and proceed with the uplinkprocedure. In another embodiment, step 818 is optional and UEs do notsend a request for remapping. The decision whether to remap UEs is madeby the BS based on aggregate information on the collisions of UEs in theCTUs. UE 104 may continue to try to resolve the collision using anasynchronous HARQ method.

FIG. 9 is a block diagram of a processing system that may be used forimplementing the devices and methods disclosed herein. Specific devicesmay utilize all of the components shown, or only a subset of thecomponents and levels of integration may vary from device to device.Furthermore, a device may contain multiple instances of a component,such as multiple processing units, processors, memories, transmitters,receivers, etc. The processing system may comprise a processing unitequipped with one or more input/output devices, such as a speaker,microphone, mouse, touchscreen, keypad, keyboard, printer, display, andthe like. The processing unit may include a central processing unit(CPU), memory, a mass storage device, a video adapter, and an I/Ointerface connected to a bus.

The bus may be one or more of any type of several bus architecturesincluding a memory bus or memory controller, a peripheral bus, videobus, or the like. The CPU may comprise any type of electronic dataprocessor. The memory may comprise any type of system memory such asstatic random access memory (SRAM), dynamic random access memory (DRAM),synchronous DRAM (SDRAM), read-only memory (ROM), a combination thereof,or the like. In an embodiment, the memory may include ROM for use atboot-up, and DRAM for program and data storage for use while executingprograms.

The mass storage device may comprise any type of storage deviceconfigured to store data, programs, and other information and to makethe data, programs, and other information accessible via the bus. Themass storage device may comprise, for example, one or more of a solidstate drive, hard disk drive, a magnetic disk drive, an optical diskdrive, or the like.

The video adapter and the I/O interface provide interfaces to coupleexternal input and output devices to the processing unit. Asillustrated, examples of input and output devices include the displaycoupled to the video adapter and the mouse/keyboard/printer coupled tothe I/O interface. Other devices may be coupled to the processing unit,and additional or fewer interface cards may be utilized. For example, aserial interface card (not shown) may be used to provide a serialinterface for a printer.

The processing unit also includes one or more network interfaces, whichmay comprise wired links, such as an Ethernet cable or the like, and/orwireless links to access nodes or different networks. The networkinterface allows the processing unit to communicate with remote unitsvia the networks. For example, the network interface may providewireless communication via one or more transmitters/transmit antennasand one or more receivers/receive antennas. In an embodiment, theprocessing unit is coupled to a local-area network or a wide-areanetwork for data processing and communications with remote devices, suchas other processing units, the Internet, remote storage facilities, orthe like.

In a first embodiment, a method comprising: implementing, by a basestation (BS), a grant-free uplink transmission scheme, wherein thegrant-free uplink transmission scheme: defines a first contentiontransmission unit (CTU) access region in a time-frequency domain;defines a plurality of CTUs; defines a default CTU mapping scheme bymapping at least some of the plurality of CTUs to the first CTU accessregion; and defines a default user equipment (UE) mapping scheme bydefining rules for mapping a plurality of UEs to the plurality of CTUs.

In a second embodiment, combing the first embodiment further comprising:defining, by the BS, at least a portion of the grant-free uplinktransmission scheme; and transmitting the portion of the grant-freeuplink transmission scheme defined by the BS using high-level signaling.

In a third embodiment, combing the first embodiment further define:wherein at least a portion of the grant-free uplink transmission schemeis pre-configured on the BS in conformance with a standard.

In a fourth embodiment, combing the first embodiment further define:wherein implementing the grant-free transmission uplink scheme furthercomprising: receiving, by the BS, an uplink transmission from a userequipment (UE); attempting to decode the uplink transmission blindly;and indicating, to the UE, whether the attempting to decode the uplinktransmission blindly was successful.

In a five embodiment, combing the first embodiment further define:wherein the grant-free uplink transmission scheme further defines asecond CTU access region in the time-frequency domain and furtherdefines the default mapping scheme by mapping the multitude of CTUs tothe first and second CTU access regions, and wherein the implementingthe grant-free transmission uplink scheme further comprises: defining,by the BS, a CTU remapping scheme by remapping a portion of theplurality of CTUs to the first and second CTU access regions when the BSdetermines a number of collisions is too frequent, wherein the BSdetermines the number of collisions is too frequent when: the BSdetermines a number times attempting to decode the uplink transmissionblindly was unsuccessful and the number of times is over a threshold; orthe BS receives a remapping request signal from the UE; and sendinginformation related to the remapping scheme using high-level signaling.

In a six embodiment, combing the first embodiment further define:wherein the default UE mapping scheme maps the UE to a first CTU, thefirst CTU being one of the plurality of CTUs, and wherein implementingthe grant-free transmission uplink scheme further comprises: defining,by the BS, a UE remapping scheme by mapping the UE to a second CTU, thesecond CTU being one of the plurality of CTUs other than the first CTU,when the BS determines a number of collisions is too frequent, whereinthe BS determines the number of collisions is too frequent when: the BSdetermines a number times attempting to decode the uplink transmissionblindly was unsuccessful and the number of times is over a threshold; orthe BS receives a remapping request signal from the UE; and sendinginformation related to the UE remapping scheme using high-levelsignaling.

In a seven embodiment, combing the first embodiment and the thirdfurther define: wherein attempting to decode the uplink transmissionblindly comprises using a joint signature and data detection using amessage passing algorithm (JMPA) method in combination with an active UEdetector method, wherein the active UE detector method comprises:receiving a list of all potential UEs; receiving a multitude of signalstransmitted over the time-frequency domain; receiving an output, fromthe JMPA method, comprising an updated list of potential UEs, whereinthe updated list includes fewer potential UEs than the list of allpotential UEs; and creating an active potential UE list in accordancewith the multitude of signals and the updated list of potential UEs.

In an eighth embodiment, combing the first embodiment further define:wherein the grant-free uplink transmission scheme defines a number ofunique pilots for grant-free uplink transmissions.

In an ninth embodiment, a base station (BS) comprising: a processor; anda computer readable storage medium storing programming for execution bythe processor, the programming including instructions to: implement agrant-free uplink transmission scheme, wherein the grant-free uplinktransmission scheme: defines a plurality of contention transmissionunits (CTUs); defines one or more CTU access regions in a time-frequencydomain; creates a default CTU mapping scheme by mapping the plurality ofCTUs to the one or more CTU access regions; and creates a default UEmapping scheme by defining rules for mapping a plurality of UEs to theplurality of CTUs; receive an uplink transmission from a user equipment(UE); attempt to decode the uplink transmission blindly; and indicate tothe UE whether the attempt to decode the uplink transmission blindly wassuccessful.

In a tenth embodiment, combing the ninth embodiment further define:wherein the plurality of CTUs comprises individual CTUs each defined asa time, frequency, signature, pilot, or a combination thereof element.

In an eleventh embodiment, combing the ten embodiment further define:The BS of claim 10, wherein each CTU is defined as a combination oftime, frequency, signature, and pilot elements, and the grant-freeuplink transmission scheme maps multiple pilot elements to eachsignature element.

In a twelve embodiment, combing the ninth embodiment further define:wherein the grant-free uplink transmission scheme defines a plurality ofCTU access regions, the plurality of CTU access regions each provide atype of service to the UE based on quality of service (QoS) level of theUE, configuration, subscribed level of service, geometry, or acombination thereof.

In a thirteenth embodiment, combing the ninth embodiment further define:wherein a size of each of the one or more CTU access regions is definedbased on an estimated probability of collisions, a number of totalcollisions over a period of time, a number of UEs supported by the BS,or a combination thereof.

In a fourteenth embodiment, combing the ninth embodiment further define:wherein a size of each of the plurality of CTUs is defined based on anexpected transmission threshold, a desired padding level, a modulationcoding scheme (MCS) level, or a combination thereof.

In a fifteenth embodiment, combing the ninth embodiment further define:wherein the grant-free uplink transmissions scheme creates a default CTUmapping in accordance with goals of distributing potential UEs uniformlyover the one or more CTU access regions and reducing a probability ofpilot collision.

In a sixteen embodiment, a method for a grant-free transmission schemecomprising: implementing, by a user equipment (UE), a default contentiontransmission unit (CTU) mapping scheme by: determining an appropriateCTU for uplink transmission in accordance with a UE mapping rule and thedefault CTU mapping scheme; and ransmitting an uplink transmission, to abase station (BS), on the appropriate CTU.

In a seventeenth embodiment, combing the sixteenth embodiment furtherdefine: further comprising, after sending an uplink transmission:determining, by the UE, whether a collision has occurred based on anindication by the BS; and resolving the collision using an asynchronoushybrid automatic repeat request (HARQ) method when the UE determines acollision has occurred.

In a eighteenth embodiment, combing the sixteenth embodiment furtherdefine: further comprising transmitting, by the UE, a remapping requestto the BS using high-level signaling when the UE determines a number ofcollisions have occurred and the number of collisions is above athreshold.

In a nineteenth embodiment, a user equipment (UE) comprising: aprocessor; and a computer readable storage medium storing programmingfor execution by the processor, the programming including instructionsto: implement a default contention transmission unit (CTU) mappingscheme by: determining an appropriate CTU for uplink transmission inaccordance with a UE mapping rule and the default CTU mapping scheme;and transmitting, to a base station (BS), an uplink transmission on theappropriate CTU; determine whether a collision has occurred based on anindication by the BS; and re-transmit, to the BS, the uplinktransmission using an asynchronous hybrid automatic repeat request(HARQ) mechanism when the UE determines a collision has occurred.

In a twenty embodiment, combing the ninteenth embodiment further define:wherein the UE mapping rule includes information for determining anappropriate CTU in accordance with a dedicated connection signature(DCS) of the UE, a DCS index, a total number of CTUs in the default CTUmapping scheme, a subframe number, or a combination thereof.

In a twenty one embodiment, combing the nineteenth embodiment furtherdefine: wherein the UE mapping rule includes information for determiningan appropriate CTU index corresponding to an index in the default CTUmapping scheme in accordance with:

ICTU=DSCi mod NCTU,

wherein ICTU is a CTU index, DSCi is a DCS index assigned to the UE bythe BS, and NCTU is a total number of CTUs in the CTU mapping scheme.

In a twenty two embodiment, combing the nineteenth embodiment furtherdefine: wherein the UE mapping rule is pre-configured on the UE.

In a twenty three embodiment, combing the nineteenth embodiment furtherdefine: wherein the UE is configured to receive the UE mapping rule fromthe BS.

In accordance with an embodiment, a method for communicating data isprovided. In this embodiment, the method includes receiving informationfrom a base station (BS) that uniquely identifies a first ContentionTransmission Unit (CTU) in a plurality of CTUs and transmitting a firstuplink data transmission to the BS without receiving an allocation ofresources from the BS according to a request/grant mechanism. The firstCTU includes a combination of time, frequency, and pilot elements, andthe first uplink data transmission is transmitted using the first CTU ina first time-frequency region. In one example, the information indicatesa configuration mapping or re-mapping of the UE to the first CTU. In thesame example, or in another example, the first CTU further comprises asignature element. In any one of the preceding examples, or in anotherexample, the information comprises a first CTU index uniquelyidentifying the first CTU in the plurality of CTUs, and wherein each CTUin the plurality of CTUs is uniquely identified by a particular CTUindex. In any one of the preceding examples, or in another example, themethod further comprises receiving high-level signaling from the BS toconfigure grant-free transmissions by the UE. In any one of thepreceding examples, or in another example, the first time-frequencyregion comprises a CTU access region configured to support contentiontransmissions by a plurality of UEs. In any one of the precedingexamples, or in another example, the method further comprisestransmitting Radio Resource Connection (RRC) signaling to the BS thatindicates a capability for grant-free transmissions. An apparatus forperforming this method is also provided.

In accordance with an embodiment, a method for communicating data isprovided. In this embodiment, the method includes sending information toa user equipment (UE) that uniquely identifies a first ContentionTransmission Unit (CTU) in a plurality of CTUs and receiving a firstuplink data transmission from the UE without sending an allocation ofresources to the UE according to a request/grant mechanism. The firstCTU includes a combination of time, frequency, and pilot elements, andthe first uplink data transmission is transmitted using the first CTU ina first time-frequency region. In one example, the information indicatesa configuration mapping or re-mapping of the UE to the first CTU. In thesame example, or in another example, the first CTU further comprises asignature element. In any one of the preceding examples, or in anotherexample, the information comprises a first CTU index uniquelyidentifying the first CTU in the plurality of CTUs, and each CTU in theplurality of CTUs is uniquely identified by a particular CTU index. Inany one of the preceding examples, or in another example, the methodfurther includes transmitting higher layer signaling to the UE, thehigher layer signaling configuring grant-free transmissions by the UE.In any one of the preceding examples, or in another example, the firsttime-frequency region comprises a CTU access region configured tosupport contention transmissions by a plurality of UEs. In any one ofthe preceding examples, or in another example, the method furtherincludes receiving Radio Resource Connection (RRC) signaling from the UEthat indicates a capability for grant-free transmissions. An apparatusfor performing this method is also provided.

In accordance with yet another embodiment, another method forcommunicating data is provided. In this embodiment, the method includesreceiving a first information from a base station (BS) via higher layersignaling that indicates a first contention transmission unit (CTU). Thefirst CTU includes a time resource, a frequency resource, and a pilotresource. The method further includes transmitting a first uplink datatransmission to the BS without using a request/grant mechanism to obtainan allocation of resources from the BS. The first uplink datatransmission is transmitted using the first CTU in a first CTU accessregion. The method further includes receiving a second information fromthe BS via higher layer signaling. The second information indicates aconfiguration re-mapping the UE to a second CTU that is different thanthe first CTU. In one example, the first information indicates aconfiguration mapping the UE to the first CTU. In the same example, orin another example, the first CTU further includes a signature resource.In any one of the preceding examples, or in another example, the secondCTU is in the first CTU access region or a second CTU access region. Inany one of the preceding examples, or in another example, the methodfurther includes receiving a message from the BS via higher layersignaling to configure grant-free transmissions by the UE. In any one ofthe preceding examples, or in another example, the first CTU accessregion is configured to support contention based transmissions by aplurality of UEs. In any one of the preceding examples, or in anotherexample, the method further includes transmitting Radio ResourceConnection (RRC) signaling to the BS that indicates a capability forgrant-free transmissions. An apparatus for performing this method isalso provided.

In accordance with yet another embodiment, another method forcommunicating data is provided. In this embodiment, the method includestransmitting a first information to a user equipment (UE) via higherlayer signaling, the first information indicating a first contentiontransmission unit (CTU). The first CTU includes a time resource, afrequency resource, and a pilot resource. The method further includesreceiving a first uplink data transmission from the UE without using arequest/grant mechanism to allocate resources to the UE. The firstuplink data transmission is transmitted using the first CTU in a firstCTU access region. The method further includes transmitting a secondinformation to the UE via higher layer signaling that indicates aconfiguration re-mapping the UE to a second CTU that is different thanthe first CTU. In one example, the first information indicates aconfiguration mapping the UE to the first CTU. In the same example, orin another example, the first CTU further includes a signature resource.In any one of the preceding examples, or in another example, the secondCTU is in the first CTU access region or a second CTU access region. Inany one of the preceding examples, or in another example, the methodfurther includes transmitting a message to the UE BS via higher layersignaling to configure grant-free transmissions by the UE. In any one ofthe preceding examples, or in another example, the first CTU accessregion is configured to support contention based transmissions by aplurality of UEs. In any one of the preceding examples, or in anotherexample, the method further includes receiving Radio Resource Connection(RRC) signaling from the UE that indicates a capability for grant-freetransmissions. An apparatus for performing this method is also provided.

In accordance with yet another embodiment, another method forcommunicating data is provided. In this embodiment, the method includesreceiving information from a base station (BS) via higher layersignaling that indicates a first contention transmission unit (CTU) thatincludes a time resource, a frequency resource, and a pilot resource,and transmitting a first uplink data transmission to the BS withoutusing a request/grant mechanism to obtain an allocation of resourcesfrom the BS for the first uplink data transmission. The first uplinkdata transmission is transmitted using the first CTU in a first CTUaccess region. In one example, the information indicates a configurationmapping or re-mapping the UE to the first CTU. In the same example, orin another example, the first CTU further includes a signature resource.In any one of the preceding examples, or in another example, theinformation comprises a UE mapping rule mapping the first CTU to the UE,and the method further includes determining the first CTU based on theUE mapping rule. In any one of the preceding examples, or in anotherexample, the method further includes receiving a message from the BS viahigher layer signaling to configure grant-free transmissions by the UE.In any one of the preceding examples, or in another example, the firstCTU access region is configured to support contention transmissions by aplurality of UEs. In any one of the preceding examples, or in anotherexample, further comprising transmitting Radio Resource Connection (RRC)signaling to the BS that indicates a capability for grant-freetransmissions. An apparatus for performing this method is also provided.

In accordance with yet another embodiment, another method forcommunicating data is provided. In this embodiment, the method includestransmitting information to a user equipment (UE) via higher layersignaling that indicates a first contention transmission unit (CTU) thatincludes a time resource, a frequency resource, and a pilot resource,and receiving a first uplink data transmission from the UE without usinga request/grant mechanism to allocate resources to the UE for the firstuplink transmission. The first uplink data transmission is transmittedusing the first CTU in a first CTU access region. In one example, theinformation indicates a configuration mapping or re-mapping the UE tothe first CTU. In the same example, or in another example, the first CTUfurther includes a signature resource. In any one of the precedingexamples, or in another example, the information comprises a UE mappingrule mapping the first CTU to the UE, and the method further includesdetermining the first CTU based on the UE mapping rule. In any one ofthe preceding examples, or in another example, the method furtherincludes transmitting a message to the UE via higher layer signaling toconfigure grant-free transmissions by the UE. In any one of thepreceding examples, or in another example, the first CTU access regionis configured to support contention transmissions by a plurality of UEs.In any one of the preceding examples, or in another example, the methodfurther includes receiving Radio Resource Connection (RRC) signalingfrom the UE that indicates a capability for grant-free transmissions. Anapparatus for performing this method is also provided.

In accordance with yet another embodiment, another method forcommunicating data is provided. In this embodiment, the method sending afirst uplink transmission to a base station (BS) without using arequest/grant mechanism to obtain a resource allocation for the firstuplink transmission from the BS. The uplink transmission is sent using afirst contention transmission unit (CTU), wherein the first CTU includesa time resource, a frequency resource, and a pilot resource. The methodfurther includes determining whether information carried by the firstuplink transmission was successfully decoded by the BS based on whetheran acknowledgement (ACK) signal associated with the first uplinktransmission is received from the BS. In one example, if no ACK signalassociated with the first uplink transmission is received from the BS,then the method further includes sending a second uplink transmission tothe BS without using a request/grant mechanism to obtain an allocationof resources from the BS. The second uplink transmission is sent using adifferent CTU than the first uplink transmission, and the second uplinktransmission carries the same information as the first uplinktransmission. In the same example, or in another example, if no ACKsignal associated with the first uplink transmission is received fromthe BS, then the method further includes determining that a number offailed decodings of the information does not exceed a threshold andsending, to the BS, a second uplink transmission to the BS of theinformation without using a request/grant mechanism to obtain anallocation of resources from the BS. The second uplink transmission issent using a different CTU than the first uplink transmission, and thesecond uplink transmission carries the same information as the firstuplink transmission. In any one of the preceding examples, or in anotherexample, the first CTU is in a first CTU access region and the secondCTU is in the first CTU access region or a second CTU access region. Inany one of the preceding examples, or in another example, the methodfurther includes receiving higher layer signaling from the BS thatindicates the first CTU. In any one of the preceding examples, or inanother example, the method further includes receiving a message fromthe BS to configure grant-free transmissions by the UE, the messagebeing received via higher layer signaling. An apparatus for performingthis method is also provided.

In accordance with yet another embodiment, another method forcommunicating data is provided. In this embodiment, the method includesreceiving a first uplink transmission from a user equipment (UE) withoutusing a request/grant mechanism to allocate resources for the firstuplink transmission to the UE and sending an acknowledgement (ACK)signal to the UE when information carried by the first uplinktransmission is successfully decoded by the BS. The first uplinktransmission is sent using a first contention transmission unit (CTU),and the first CTU includes a time resource, a frequency resource, and apilot resource. The ACK signal indicates that the information carried bythe first uplink transmission was successfully decoded. In one example,the method further includes determining that the information carried bythe second uplink transmission cannot be successfully decoded by the BS,and based thereon receiving a second uplink transmission from the UEwithout using a request/grant mechanism to allocate resources for thesecond uplink transmission to the UE, wherein the second uplinktransmission is sent using a different CTU, and wherein the seconduplink transmission carries the same information as the first uplinktransmission. In such an example, the method may further include sendinghigher layer signaling to the UE that indicates a different CTU. In anyone of the preceding examples, or in another example, the first CTU isin a first CTU access region and the different CTU is in the first CTUaccess region or a different CTU access region. In any one of thepreceding examples, or in another example, the method further includessending higher layer signaling to the UE that indicates the first CTU.An apparatus for performing this method is also provided.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A method for a user equipment (UE) comprising:sending, by the UE, a first uplink transmission to a base station (BS)without using a request/grant mechanism to obtain a resource allocationfor the first uplink transmission from the BS, wherein the uplinktransmission is sent using a first contention transmission unit (CTU),wherein the first CTU includes a time resource, a frequency resource,and a pilot resource; and determining, by the UE, whether informationcarried by the first uplink transmission was successfully decoded by theBS based on whether an acknowledgement (ACK) signal associated with thefirst uplink transmission is received from the BS.
 2. The method ofclaim 1, further comprising: if no ACK signal associated with the firstuplink transmission is received from the BS, sending, to the BS, asecond uplink transmission to the BS without using a request/grantmechanism to obtain an allocation of resources from the BS, wherein thesecond uplink transmission is sent using a different CTU than the firstuplink transmission, and wherein the second uplink transmission carriesthe same information as the first uplink transmission.
 3. The method ofclaim 1 further comprising: if no ACK signal associated with the firstuplink transmission is received from the BS, determining that a numberof failed decodings of the information does not exceed a threshold andsending, to the BS, a second uplink transmission to the BS of theinformation without using a request/grant mechanism to obtain anallocation of resources from the BS, wherein the second uplinktransmission is sent using a different CTU than the first uplinktransmission, and wherein the second uplink transmission carries thesame information as the first uplink transmission.
 4. The method ofclaim 3, wherein the first CTU is in a first CTU access region and thesecond CTU is in the first CTU access region or a second CTU accessregion.
 5. The method of claim 1 further comprising receiving, by theUE, higher layer signaling from the BS that indicates the first CTU. 6.The method of claim 1, further comprising: receiving, by the UE, amessage from the BS to configure grant-free transmissions by the UE, themessage being received via higher layer signaling.
 7. A user equipment(UE) comprising: a processor; and a computer readable storage mediumstoring programing for execution by the processor, the programmingincluding instructions to: send a first uplink transmission to a basestation (BS) without using a request/grant mechanism to obtain aresource allocation for the first uplink transmission from the BS,wherein the uplink transmission is sent using a first contentiontransmission unit (CTU), wherein the first CTU includes a time resource,a frequency resource, and a pilot resource; and determine whetherinformation carried by the first uplink transmission was successfullydecoded by the BS based on whether an acknowledgement (ACK) signalassociated with the first uplink transmission is received from the BS.8. The UE of claim 7, wherein the programming includes furtherinstructions to: if no ACK signal associated with the first uplinktransmission is received from the BS, sending, to the BS, a seconduplink transmission to the BS without using a request/grant mechanism toobtain an allocation of resources from the BS, wherein the second uplinktransmission is sent using a different CTU than the first uplinktransmission, and wherein the second uplink transmission carries thesame information as the first uplink transmission.
 9. The UE of claim 7,wherein the programming includes further instructions to: if no ACKsignal associated with the first uplink transmission is received fromthe BS, determining that a number of failed decodings of the informationdoes not exceed a threshold and sending, to the BS, a second uplinktransmission to the BS of the information without using a request/grantmechanism to obtain an allocation of resources from the BS, wherein thesecond uplink transmission is sent using a different CTU than the firstuplink transmission, and wherein the second uplink transmission carriesthe same information as the first uplink transmission.
 10. The UE ofclaim 9, wherein the first CTU is in a first CTU access region and thesecond CTU is in the first CTU access region or a second CTU accessregion.
 11. The UE of claim 7, wherein the programming includes furtherinstructions to receive higher layer signaling from the BS thatindicates the first CTU.
 12. A method comprising: receiving, by a basestation (BS), a first uplink transmission from a user equipment (UE)without using a request/grant mechanism to allocate resources for thefirst uplink transmission to the UE, wherein the first uplinktransmission is sent using a first contention transmission unit (CTU),wherein the first CTU includes a time resource, a frequency resource,and a pilot resource; and sending, by the BS, an acknowledgement (ACK)signal to the UE when information carried by the first uplinktransmission is successfully decoded by the BS, the ACK signalindicating that the information carried by the first uplink transmissionwas successfully decoded.
 13. The method of claim 12, furthercomprising: determining that the information carried by the seconduplink transmission cannot be successfully decoded by the BS, and basedthereon receiving a second uplink transmission from the UE without usinga request/grant mechanism to allocate resources for the second uplinktransmission to the UE, wherein the second uplink transmission is sentusing a different CTU, and wherein the second uplink transmissioncarries the same information as the first uplink transmission.
 14. Themethod of claim 13 further comprising: sending, by the BS, higher layersignaling to the UE that indicates a different CTU.
 15. The method ofclaim 14, wherein the first CTU is in a first CTU access region and thedifferent CTU is in the first CTU access region or a different CTUaccess region.
 16. The method of claim 12 further comprising: sending,by the BS, higher layer signaling to the UE that indicates the firstCTU.
 17. A base station (BS) comprising: a processor; and a computerreadable storage medium storing programing for execution by theprocessor, the programming including instructions to: receive a firstuplink transmission from a user equipment (UE) without using arequest/grant mechanism to allocate resources for the first uplinktransmission to the UE, wherein the first uplink transmission is sentusing a first contention transmission unit (CTU), wherein the first CTUincludes a time resource, a frequency resource, and a pilot resource;and send an acknowledgement (ACK) signal to the UE when informationcarried by the first uplink transmission is successfully decoded by theBS, the ACK signal indicating that the information carried by the firstuplink transmission was successfully decoded.
 18. The BS of claim 17,wherein the programming includes further instructions to: determine thatthe information carried by the second uplink transmission cannot besuccessfully decoded by the BS, and based thereon receiving a seconduplink transmission from the UE without using a request/grant mechanismto allocate resources for the second uplink transmission to the UE,wherein the second uplink transmission is sent using a different CTU,and wherein the second uplink transmission carries the same informationas the first uplink transmission.
 19. The BS of claim 18, wherein theprogramming includes further instructions to: send to the UE higherlayer signaling to the UE that indicates a different CTU.
 20. The BS ofclaim 18, wherein the first CTU is in a first CTU access region and thedifferent CTU is in the first CTU access region or a different CTUaccess region.